Advanced oxidation processes for destruction of cyanide from thermoelectric power station waste waters

Several advanced oxidation processes for the destruction of cyanide contained in waste waters from thermoelectric power stations of combined-cycle were studied. Thus, oxidation processes involving ozonation at basic pH, ozone/hydrogen peroxide, ozone/ultraviolet radiation and ozone/hydrogen peroxide/ultraviolet radiation have been carried out in a semi-batch reactor. All these methods showed that total cyanide can be successfully degraded but with different reaction rates, and the decrease in the total cyanide concentration can be described by pseudo-first order kinetics. The influence of pH and initial concentration of hydrogen peroxide was studied to find the optimal conditions of the oxidation process. Experimental results of the single ozone treatment indicated that total cyanide is destroyed more rapidly at higher pH (12), while ozonation combined with H2O2 and/or UV is faster at pH 9.5. The optimum concentration of H2O2 was 20.58 x 10(-2) M because an excess of peroxide decreases the reaction rate, acting as a radical scavenger. The total cyanide degradation rate in the O-3/H2O2(20.58 x 10(-2) M) treatment was the highest among all the combinations studied. However, COD reduction, in the processes using UV radiation such as O-3/UV or O-3/H2O2/UV was about 75%, while in the processes with H2O2 and/or O-3/H2O2 was lower than 57% and was insignificant, when using ozone alone. (C) 2004 Society of Chemical Industry.